New plans for the Millbrook Crossing development call for 46 affordable-housing apartments and 7,000 square feet of commercial space.

Gareth Orsmond, an attorney for the project’s developers, told Duxbury selectmen Monday night that the tentative plans are for apartments with one, two and three bedrooms. Most would be two-bedroom units, he said.

The original proposal by resident Ben Goodrich and Silvia & Silvia Associates, a custom builder, to redevelop 6.2 acres at St. George Street and Railroad Avenue was rebuffed last year when the board of health refused to approve an above-ground septic system. The board does not allow such “mounded” systems for new developments.

Orsmond assured selectmen that the new proposal, submitted under the state’s affordable-housing law known as Chapter 40B, would generate less than 10,000 gallons of sewage per day.

Although he said it was too early to say how sewage disposal would work at the site, but he also said he did not see how mounding could be avoided.

If the board of health has to be asked for a waiver for a mounded system, “we’ll do everything we can do to design it in the safest way possible,” Orsmond said.

He said Millbrook Crossing’s planners envision tearing down the building that houses Millbrook Market and putting up a similar building that has housing above businesses, including the market. Orsmond called it a “smart-growth” plan.

The old Goodrich Lumber building near the midpoint of Railroad Avenue would be razed and replaced with a two-story apartment building. The existing structure is “deteriorating tremendously,” Orsmond said.

Selectmen Andre Martecchini and Elizabeth Sullivan said they would like to see more commercial space in the project. Sullivan emphasized that the area has historically been commercial.

Also at the meeting, Town Manager Richard MacDonald announced that Standard & Poor’s will upgrade Duxbury’s bond rating from AA+ to AAA, the highest rating possible.

“It’s a great, great step for us, and I’m proud of it,” MacDonald said.